A "layer" refers to a single thickness or stratum of material that is stacked or placed over another. Layers can be found in various contexts, such as in geology, where different types of rock form distinct layers over time, or in cooking, where ingredients are arranged in layers, like in a lasagna. In technology, layers are used in software design, where each layer serves a specific function, allowing for better organization and management of complex systems. For example, in the OSI model, each layer represents a different aspect of network communication, facilitating data transfer between devices.